Steel 1.4512 is commonly used in the form of hot rolled bars. The manufacturing of such bars sometimes leads to the formation of edge defects. In this paper, the origin of some edge defects occurring during hot rolling of flat bars is analyzed. Thermomechanical and microstructural evolution calculations have been performed aimed to put in evidence its effect on the product quality and reducing the jagged borders defect on hot rolled bars. A deep investigation has been carried out by analyzing the defects on the final product from both the macroscopic and microstructural point of view through the implementation of thermomechanical and metallurgical models in a Finite Element (FE) MSC.Marc commercial code. Coupled metallurgical and damage models have been implemented to investigate the microstructural evolution of ferritic grain size and material damaging. Three levels of Prior Ferritic Grain Size (PFGS) and three furnace discharge temperatures have been considered in the thermo-mechanical simulations of the roughing passes. Rheological laws for modelling the evolution of ferritic grain have been modified to describe the specific cases simulated. Results have shown that the defect is caused by processing conditions that trigger an anomalous heating which, in turn, induces an uncontrolled grain growth on the edges. The work-hardened and elongated grains do not recrystallize during hot deformation. Consequently, they tend to squeeze out the surrounding softer and recrystallized matrix towards the edges of the bar where the fractures that characterizes the surface defect occur.

Microstructure evolution after hot plastic deformation in ferritic stainless steels: a modelling tool to reduce defects in steel bars

Andrea Di Schino
2022

Abstract

Steel 1.4512 is commonly used in the form of hot rolled bars. The manufacturing of such bars sometimes leads to the formation of edge defects. In this paper, the origin of some edge defects occurring during hot rolling of flat bars is analyzed. Thermomechanical and microstructural evolution calculations have been performed aimed to put in evidence its effect on the product quality and reducing the jagged borders defect on hot rolled bars. A deep investigation has been carried out by analyzing the defects on the final product from both the macroscopic and microstructural point of view through the implementation of thermomechanical and metallurgical models in a Finite Element (FE) MSC.Marc commercial code. Coupled metallurgical and damage models have been implemented to investigate the microstructural evolution of ferritic grain size and material damaging. Three levels of Prior Ferritic Grain Size (PFGS) and three furnace discharge temperatures have been considered in the thermo-mechanical simulations of the roughing passes. Rheological laws for modelling the evolution of ferritic grain have been modified to describe the specific cases simulated. Results have shown that the defect is caused by processing conditions that trigger an anomalous heating which, in turn, induces an uncontrolled grain growth on the edges. The work-hardened and elongated grains do not recrystallize during hot deformation. Consequently, they tend to squeeze out the surrounding softer and recrystallized matrix towards the edges of the bar where the fractures that characterizes the surface defect occur.
2022
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/1494840
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